"Engineer" wrote
...
So, what primary impedance should the replacement OPT have? 6000,
10000 ohms, other? I don't mind re-engineering the O/P stage to
get
a genuine 10 watts in class AB1, or close enough. I've not yet
drawn
load lines on 6V6 plate curves, it may come to that, but two 6V6's
are
such an established design that it should be a no-brainer to pick
the
best OPT primary impedance.
...

http://tdsl.duncanamps.com/show.php?des=6V6

Look at application data. Although for pentode, triode or UL will be
much the same. See eg

http://tdsl.duncanamps.com/pdf/6v6vm.pdf

which shows examples for triode connection.

cheers, Ian